With respect to a production method of an allophanate group-containing polyisocyanate composition, mainly two methods are well known. That is, there are known a process wherein an urethane group-containing organic compound and an isocyanate group-containing organic compound are allowed to react with each other under heating, and a process wherein reaction between an urethane group-containing organic compound and an isocyanate group-containing organic compound is carried out by using an allophanation catalyst, which are disclosed in British Patent No. 994,890, JP-A 46-1671, JP-A 64-66155, JP-A 7-304728 and JP-A 8-188566.
In British Patent No. 994,890, there is disclosed a process wherein a mixture of a mono- or polyhydric alcohol and a diisocyanate is subjected to allophanation by heating or using an allophanation catalyst according to the above-mentioned process. In said British Patent, a carboxylate of a metal such as zirconium, a metal chelate and a tertiary amine are disclosed as the allophanation catalyst. However, there is no description relating to the zirconyl compound and the zirconium alcoholate specified in the present invention.
Further, in Examples of said British Patent, there are disclosed a process wherein heating is carried out at 130 to 135° C. for 24 hours to complete an allophanation reaction of hexamethylene diisocyanate, and a process wherein using a tertiary amine or a zinc carboxylate as the allophanation catalyst, reaction is carried out at room temperature to 50° C. for 69 to 89 hours. However, according to these processes, not only the allophanate group-containing polyisocyanate composition, but also an urethodione group- or isocyanurate group-containing polyisocyanate composition is produced to a considerable extent. Moreover, the obtained polyisocyanate composition is considerably colored.
Furthermore, in said British Patent, there is no disclosure of any condition under which a polyisocyanate composition high in a production ratio of an allophanate group can be produced. According to the present inventors' follow-up examination, the production ratio of an allophanate group was found to be about 45 to 60% when zinc carboxylate was used.
In JP-A 46-1671, there is disclosed a process wherein an isocyanate compound having an isocyanate group bound to at least one aromatic ring is subjected to allophanation in the presence of a compound having an alkylation ability as the allophanation catalyst, and if necessary, further in the presence of a Group III, IV-A, II, VI or VII-B metal compound. As an example of the metal compound, zirconium tetrapropiolate is disclosed in said Japanese Patent Application, and in Examples thereof, zirconium acetylacetonate (tetrakis(2,4-pentanedionate) zirconium (IV)) is used. However, this compound is only added complementarily to the alkylation ability-having compound of the allophanation catalyst. Further, the present inventors have confirmed that an allophanation reaction does not proceed with the aid of the zirconium acetylacetonate. Furthermore, in said Japanese Patent Application, it is noted that application of an isocyanate other than an isocyanate group bound to an aromatic ring is excluded. Thus, JP-A 46-1671 is entirely silent about the fact that an aliphatic or alicyclic diisocyanate, and either a zirconyl compound or a zirconium alcoholate as specified in the present invention are used as a starting material and the allophanation catalyst, respectively, thereby producing an allophanate group-containing polyisocyanate composition.
In JP-A 64-66155, there is disclosed a process comprising carrying out heating at a high temperature for a short period of time without use of the allophanation catalyst, thereby attaining a relatively limited amount of coloration and diminishing the formation of urethodione to an extreme degree. However, in said Japanese Patent Application, it is disclosed that the production ratio of the allophanate group is not always high.
In JP-A 7-304728, an allophanation catalyst having a tin compound is disclosed, and it is disclosed that the tin compound is used as the allophanation catalyst to obtain an allophanate group-containing polyisocyanate composition. However, in JP-A 7-304728, there is no disclosure concerning the zirconyl compound and the zirconium alcoholate specified in the present invention.
In JP-A 8-188156, there is disclosed a process comprising using an organic metal carboxylate and an organic phosphorous acid ester as the allophanation catalyst. In said Japanese Patent Application, it is disclosed that according to the reaction using the organic metal carboxylate and the organic phosphorous acid ester, a polyisocyanate composition substantially free from urethodionation or isocyanuration is produced. However, in said JP-A 8-188156, there is no disclosure that the zirconyl compound or the zirconium alcoholate specified in the present invention is used as the allophanation catalyst, and in all of the Examples thereof, a lead compound is used as the allophanation catalyst.
On the other hand, in JP-A 61-151179, there is disclosed an isocyanuration reaction. In the Example thereof, zirconium butoxide is used as a catalyst for the isocyanuration. However, when the polyisocyanate composition was produced according to the process disclosed in said Example, the production ratio of the allophanate group was found to be at most about 10%.